All 3D printing is based on printing one layer of a build on top of another, this works fine when you’re building straight up but if you have a structure that widens or has bridges you can end up with an overhang that may not get enough support from the rest of the material. To make sure overhangs stay in place, support structures are used. These are 3D printed structures that are designed to provide support during the printing process and then be removed from the finished print.
Not all overhangs need support structures, the 45° rule is a good guideline to follow, with overhangs that are more than 45° from the vertical needing support. This can vary between printers, slicing software, filaments, and settings, however, so your results may vary. If you do need support structures, most slicing software offers settings that can automatically generate support structures for you. Generally, you’ll be able to choose where your support structures are placed with the option for everywhere and “touching build plate”. As removing support structures can leave artifacts on the print, you may want to choose to only print support structures that can build directly of the build plate to minimise the effect on the surface of the print, depending on your print’s structure, however, this may not provide enough support.
The support pattern can have a large effect on the structural integrity of the support, with lines and zigzags being generally favoured as they’re easy to remove. If some more strength is needed grid and triangle patterns can be a great choice if you’re willing to have your print take longer, use more materials, and have them be more hassle to remove. For circular structures such as spheres and cylinders, concentric support structures are often the best option. Support towers or trees are also an option that provide a totally different support shape, they typically have a large support trunk that specifically tapers at the contact point with the print, they can also have branches coming off them to provide support to other nearby areas. This design gives them good rigidity and minimal contact with the print.
Support density is similar to infill density, allowing you to make support structures such as grids tighter to provide more structural integrity. Higher density structures can provide more support, however, they also require more filament, take more time to print, and increase the difficulty of post-processing due to the increased contact with the print. Support densities between 5 and 20% are typical.
Horizontal expansion is a useful option if you’re trying to provide support for very narrow, bridges or overhangs. If the support structure itself Is too narrow, it may not be able to provide enough support or potentially even just crumble away. Horizontal expansion widens support structures, though this will obviously end up using more material and taking longer.
Soluble support structures
Typically support structures are printed from the same material as the print, however, 3D printers that support printing with two independent print heads during one print can allow you to change this up. While they tend to be more expensive than normal filaments you can buy filaments such as PVA or HIPS, which can simply be dissolved away once the print is complete. This can take time but leaves the print itself unscarred by cutting or sanding artifacts. Soluble support structures can even allow you to print previously unprintably complex internal geometry as you don’t need to worry about being able to reach in to be able to cut the support away. PVA is best paired with PLA as they are printed at similar temperatures and PLA is hydrophobic, which is a useful feature given that PVA dissolves in water. HIPS is generally paired with ABS, again due to the similarities in printing temperatures, furthermore, ABS is one of the few materials that won’t be damaged by the limonene used to dissolve HIPS.